1. Field of the Invention
The present invention relates to a photoelectric conversion device formed by using a crystal layer which is formed by a crystal growth method for selectively growing a crystal with the aid of a difference of nucleation densities between a deposition film forming material and a surface material on which a deposition film is formed.
2. Related Background Art
Research and development on a three-dimensional integrated circuit are now being vigorously pursued to achieve high integration and multi-functions by laying semiconductor elements one upon another in the vertical direction of the substrate.
To fabricate a three-dimensional integrated circuit, it is necessary to form on an amorphous insulator a semiconductor thin film in which electronic elements such as transistors are formed. However, in general, only amorphous silicon or polysilicon can grow on an amorphous material.
Therefore, amorphous silicon or polysilicon have been used heretofore as a semiconductor layer for electronic elements, or alternatively monocrystalline silicon has been used which is formed by melting and monocrystallizing grown amorphous silicon or polysilicon with a laser beam.
Use of amorphous silicon or polysilicon as a semiconductor layer for electronic elements, however, results in a low electron mobility: lower than 0.1 cm.sup.2 /V sec for amorphous silicon and 1 to 10 cm.sup.2 /V sec for polysilicon having a grain diameter of several hundreds angstroms. In addition, a large leakage current flows through a PN junction. Thus, electronic elements having a good performance cannot be realized.
Apart from the above, since a monocrystalline silicon layer is used as a semiconductor layer in the method of melting and monocrystallizing the amorphous silicon or polysilicon, electronic elements of good performance can be realized. However, heating and melting with a laser beam greatly influence the performance of elements formed in an under layer.